hey everyone, so finally after getting the important mechanical issues fixed with the car I have left some luxury items to tend to.

Im turning my attention to the AC unit and first off I notice the compressor will not click on, and after checking the leads, it doesnt have voltage to turn on. I read that there is a pressure switch on the circut that keeps the compressor off if theres nothing in the system. I want to recharge the system but will the standard (I think R134a?) refridgerant work in this car or do I need to change fittings to use it? I already checked the fuse, and im not sure what relay is the correct one, (though I did find out one of the silver box relays runs rather hot...) could that be it?
By the way its a 1985 300SD with 193,000 miles.
Thanks for the help!